In the field of internal combustion engines, water-cooled engines have been adopted very extensively. In such engines cooling water is pumped in a closed circuit with the aid of a coolant pump through cooling passages in the region of the cylinders in order to cool the internal combustion engine, and is then conveyed to an air/water radiator where the heated water is cooled down by means of the air stream generated by vehicle motion. In this case the pump needed to circulate the water is usually connected via a belt to a pulley of the crankshaft of the internal combustion engine.
The direct coupling between coolant pump and crankshaft ensures that the rotational speed of the pump is dependent on the rotational speed of the internal combustion engine. This has the result that in the high rotational speed range of the internal combustion engine a correspondingly large volume flow is made available by the pump, in an amount which is not required for cooling. By contrast, upon cold starting of the internal combustion engine the problem arises that coolant is already circulating through the cooling passages, which hinders the heating of the combustion chambers and therefore delays the attainment of an optimum operating temperature.
In view of these facts, in modern internal combustion engines use is frequently made of variable coolant pumps the delivery rate of which can be adjusted according to demand.
Known from DE 10 2005 004 315 B4 is a variable coolant pump in which an impeller and a cover disc are provided on a hollow shaft mounted in a pump housing in order to convey water aspirated via a pressure connection piece into an annular passage of the pump housing. In addition, a slide element located behind the impeller is mounted on the hollow shaft and is displaceable against a spring by means of an electromagnet in the direction of the impeller. In this case the slide element has in its outer region axially disposed projections which extend beyond the impeller and with which, upon displacement of the slide element in the direction of the impeller, the annular passage of the pump housing is closed and pumping of the cooling water by the coolant pump is therefore prevented.
A disadvantage of such an arrangement is that the system for regulating the coolant flow by means of the slide element involves a complex and costly mechanism and therefore a complicated structure. Moreover, as a result of the orientation of the projections of the slide element, strong turbulence is generated in the region of the annular passage of the pump housing when the pump is partially open.
It is therefore the object of the present invention to provide a variable coolant pump for a cooling circuit of an internal combustion engine which has a simple structure and which, even with partial delivery, tends to produce only vanishingly small turbulence.